1. Field of the Invention
The present invention relates to an ionized PVD device and a method for manufacturing a semiconductor device, and more particularly to an ionized PVD device capable of performing film formation having excellent vertical growth, and a method for manufacturing a semiconductor device using the ionized PVD device.
2. Description of the Background Art
With reference to FIG. 9, a structure of a conventional ionized PVD (Physical Vapour Deposition) device 90 will be described below. FIG. 9 is a schematically sectional view for explaining the structure of the ionized PVD device 90.
As shown in FIG. 9, the ionized PVD device 90 comprises a cylindrical vacuum chamber 20 having a bottom and a cover in which a high-frequency coil (RF coil) 21, a sputtering target 22 and a wafer susceptor 23 are incorporated.
The high-frequency coil 21 is provided in a central portion of the vacuum chamber 20 such that a direction of a central axis thereof is coincident with that of a central axis of the vacuum chamber 20. Both ends of the high-frequency coil 21 are electrically connected to a high-frequency power supply R1 and a ground potential GND through current introducing terminals (feedthrough terminals) 24A and 24B provided on a side wall section 201 of the vacuum chamber 20.
The sputtering target 22 is attached to a cover section 202 which is electrically insulated from the side wall section 201 of the vacuum chamber 20 through an electric insulator 25, and is electrically connected to a negative output terminal of a DC power supply D1 through the cover section 202. The side wall section 201 and a bottom section 203 of the vacuum chamber 20 are electrically connected to a ground potential GND.
A peripheral portion of the sputtering target 22 is covered with a dark space shield 27.
A wafer 30 is mounted on the wafer susceptor 23. The wafer susceptor 23 serves to apply a high-frequency bias to the wafer 30, and includes a table 231 for mounting the wafer 30 thereon, and a strut 232 for supporting the table 231. The strut 232 is connected to a high-frequency power supply R2 through the bottom section 203 of the vacuum chamber 20, and is electrically insulated from the bottom section 203 by an electric insulator 26.
Operation of the ionized PVD device 90 will be described below with reference to FIG. 9.
First of all, the vacuum chamber 20 is sealed to exhaust air in the vacuum chamber 20 from an exhaust port which is not shown and to reduce a pressure of the vacuum chamber 20 to a predetermined value. Then, a rare gas such as an argon gas is introduced into the vacuum chamber 20 through a gas inlet which is not shown to raise the pressure of the vacuum chamber 20 to a predetermined value.
The sputtering target 22 is electrically connected to the negative output terminal of the DC power supply D1 through the cover section 202. For this reason, when a voltage is applied from the DC power supply D1, the sputtering gate 22 functions as a cathode. Since the side wall section 201 of the vacuum chamber 20 is connected to the ground potential GND, it functions as an anode. When an output voltage of the DC power supply D1 reaches a predetermined value, a plasma AP is produced in the vacuum chamber 20.
Argon ions in the plasma AP collide with the sputtering target 22 which acts as a negative potential, and sputter a component of the sputtering target 22, for example, titanium (Ti) as neutral atoms or titanium ions. A material of the sputtering target 22 is determined according to a composition of a desired film to be formed on the wafer 30 which will be described below.
The high-frequency coil 21 is provided so as to surround a region where the plasma AP is formed. A high-frequency current is caused to flow from the high-frequency power supply R1 to the high-frequency coil 21 so that an induction field is formed in the plasma AP. Electrons in the plasma AP are accelerated by the induction field. Consequently, a density (an ionization degree) of the plasma can be increased by ionization function of the accelerated electrons.
The neutral atoms or ions of titanium sputtered from the sputtering target 22 enter the plasma AP, and the neutral atoms are ionized by the accelerated electrons.
The titanium ions move in the plasma AP to approach the wafer 30. A wafer-plasma DC electric field which is induced by a high-frequency voltage applied from the high-frequency power supply R2 to the wafer 30 through the wafer susceptor 23 is present between a surface of the wafer 30 and the plasma AP. Consequently, the titanium ions are accelerated by the DC electric field and are caused to be incident on the wafer 30 almost perpendicularly.
If the titanium ions are incident on the wafer 30 almost perpendicularly, film formation having excellent bottom coverage can be performed in which a titanium film is formed on only a bottom of a vertical contact hole formed on the wafer 30, and is not formed on a wall of the contact hole.
If a rate of a metal film formed by neutral metal atoms incident on the wafer 30 with a great angular spread is higher than that of a metal film formed by metal ions incident on the wafer 30 perpendicularly, vertical growth is poor so that the bottom coverage is deteriorated.
More specifically, the metal film is formed on the wall of the contact hole as well as the bottom portion thereof. Consequently, the contact hole is blocked.
The neutral metal atoms which cause the above-mentioned state exist in the plasma AP. As described above, the neutral metal atoms are supplied from the sputtering target 22. However, about several percent of the neutral metal atoms are ionized. Accordingly, the neutral metal atoms exist more than the metal ions in the plasma AP.
While all the neutral metal atoms are not incident on the wafer 30, at least the neutral metal atoms having a speed component in a wafer direction are incident on the wafer 30. The ionized PVD device 90 described above does not have a structure in which the neutral metal atoms are prevented from being incident on the wafer 30.
If an ionization ratio of the neutral metal atoms can be increased rapidly, an influence of the neutral metal atoms can be reduced. However, the high-frequency coil 21 incorporated in the ionized PVD device 90 is not perfect. A mechanism for producing a plasma by arc discharge and a structure for supplying the neutral metal atoms by a method other than sputtering should be required so that a structure of a device becomes complicated.